A driveline of a vehicle may include a torque converter that provides torque multiplication and driveline dampening. The torque multiplication can improve vehicle acceleration from zero speed, but the torque multiplication is a result of operating an engine or motor at a higher speed to create slip across the torque converter. The engine, motor, and torque converter may operate less efficiently when there is a large amount of slip across the torque converter (e.g., a large speed differential between a torque converter impeller and torque converter turbine). Consequently, powertrain efficiency may be reduced more than is desired during vehicle launch. Nevertheless, it may be desirable for the torque converter to operate with a large amount of slip between the torque converter impeller and the torque converter turbine when a driver is requesting a large amount of torque so that the vehicle may accelerate more rapidly.
The inventors herein have recognized the above-mentioned issue and have developed a driveline operating method, comprising: accelerating a torque converter impeller to a desired speed responsive to release of a brake pedal during a vehicle launch; providing hydraulic and friction torque paths through a torque converter in response to driver demand less than a threshold during the vehicle launch; and providing only a hydraulic torque path through the torque converter in response to driver demand greater than the threshold during the vehicle launch.
By selectively providing different torque paths through a torque converter during vehicle launch, it may be possible to provide the technical result of improved torque converter and driveline efficiency. In particular, driver demand may be a basis for deciding whether torque is passed through a torque converter during vehicle launch via only a hydraulic torque path or via hydraulic and friction torque paths. The hydraulic and friction torque paths may be provided for lower driver demand conditions while only the hydraulic torque path is provide during higher driver demand conditions.
Additionally, compensation may be provided for torque converter lockup clutch delay periods so that driveline torque response may be improved. For example, torque converter impeller speed or torque may be adjusted during the torque converter lockup clutch delay period to temporarily increase torque flow through the torque converter hydraulic torque path so as to improve the amount of torque transferred to a transmission and vehicle wheels.
The present description may provide several advantages. For example, the approach may provide more consistent vehicle launches under similar operating conditions. Additionally, the approach may improve driveline efficiency while at the same time providing the capacity to accelerate at a higher rate when requested by driver demand. Further, the approach compensates for delays in torque converter clutch lockup operation so that a driver may experience a more acceptable rate of vehicle acceleration.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.